The present invention relates to drug delivery systems and, in particular, it concerns a fluid flow regulator for regulating the flow of liquid medications.
In many cases, it is desired to administer a fluid medication continuously at a slow rate over a given time period. The most common technique for doing this is by adding the medication to a relatively large amount of physiologically compatible liquid and delivering the resulting mixture through an infusion.
This approach suffers from a number of disadvantages. Firstly, the amounts of liquids generally used may in certain cases cause medical complications. Secondly, the presence of an infusion greatly limits the mobility of the patient. And thirdly, the rate of delivery of the mixture may be imprecise, depending both upon the ability of the operator to correctly adjust the flow rate and on the liquid level within the infusion bag. The problem of precision may be addressed by use of an electromechanical dosage regulator. This, however, is a relatively expensive solution, and does not address the remaining problems mentioned above.
An alternative approach to slow drug delivery is by absorption through the skin by use of adhesive patches. This approach, however, gives very non-uniform dosage, and can only deliver very small quantities of medication.
In an attempt to achieve more uniform dosages at a wide range of flow rates, flow regulators have been developed based on the use of a pressure-responsive flexible diaphragm. The principle of these regulators may be understood by reference to U.S. Pat. Nos. 4,343,305 and 5,421,363 to Dan Bron which are hereby incorporated by reference. The Bron '305 reference discloses a flow regulator for use in an infusion set. The flow regulator includes a body having a cavity divided into two chambers by a flexible diaphragm. The first of these chambers is a pressure sensing chamber. The other is a valving chamber through which the drug flows, the outlet from that chamber being centrally disposed underlying the diaphragm whereby flexing of the diaphragm in one direction as a result of increased pressure in the other chamber adjusts the size of the flow path through the outlet. A rudimentary flow impedance adjustment between the two chambers is proposed as a means for adjusting the flow rate.
The Bron '363 reference proposes an improved adjustment configuration in which a tubular flow attenuator fits within the neck portion of a housing. The flow attenuator is formed with a pattern of grooves which, together with the opposing surface, define a meander-type labyrinth. The relative positions of an inlet and outlet along the labyrinth may be varied by relative rotation between the flow attenuator and the neck portion, thereby changing the operative length of the labyrinth and the consequent flow rate.
The diaphragm-based regulators of Bron provide significant advantages over the slow-dosing techniques described above. Specifically, these regulators provide generally uniform dosing of medication at low flow rates, thereby avoiding the need for the excessive dilution of conventional infusions. The pressure-responsive nature of the regulation also ensures that supply pressure variations are properly compensated. Nevertheless, these regulators suffer from a number of serious shortcomings. Most notably, the full range of adjustment, even for the improved configuration of the '363 patent, corresponds to a range of rotation significantly less than a full revolution. As a result, the regulator is either implemented so as to be limited to a fairly narrow range of flow rates or is overly sensitive to angular displacements offering a low degree of precision in selecting the flow rate.
A further shortcoming of the aforementioned Bron regulators is the complexity of manufacturing high-precision meandering labyrinth grooves around the internal surface of a cylindrical element.
U.S. Pat. No. 5,101,854 also to Bron discloses an alternative design of diaphragm-based flow regulator which employs a flow-attenuating passageway formed by opposing surfaces one of which has a helical groove. The use of a helical groove provides considerable advantages of ease of production and precision. However, no provision is offered for rendering such a helical flow-attenuating passageway adjustable. Instead, adjustment is achieved by changing the outlet geometry directly by raising or lowering the outlet aperture relative to the diaphragm.
Finally, it should be noted that all of the above-mentioned regulators must be connected at all times to an external supply of medication, rendering the drug delivery system a minimum of at least two separate parts and somewhat bulky.
There is therefore a need for a simple diaphragm-based flow regulator, suitable for use in medical applications, which would provide precise control of the flow rate over a wide range of rates. It would also be advantageous to provide a compact drug delivery device which would provide pressure-responsive regulation of drug release from a contained volume.